A computer application can store and access data by sending queries to, and receiving replies from, a database system. As an application's storage or query processing requirements increase, a single database system may be unable to adequately support the application. In such a case, the application may use multiple database systems. Each database system can store a portion of the data needed by the application. An application may then distribute its queries among the multiple database systems, thus enabling a larger volume of queries to be processed.
To support multiple databases, an application may need to be programmed with knowledge of the various database systems and the distribution of its data among those systems. Such programming may complicate application development and may complicate reconfiguration of the database systems. Consequently, improvements in the use of multiple database systems are desired.